Process and apparatus for transporting mined deposits from the sea floor

ABSTRACT

Air is withdrawn from an air lift hydraulic pipe to control turbulence and velocity of flow through the pipe. The air is withdrawn at a location substantially above the air injection station where the expanding air causes excessively high velocity and turbulence which cause nodule breakage and wear of the pipe. In one embodiment a sleeve valve is used to selectively open perforations communicating with the interior of the pipe. The body of the valve can be connected to a vacuum source at the surface to increase the amount of air removed from the pipe. In a second embodiment a perforated member is located within the pipe and flow of air to the outside of the pipe is controlled by valves. The valves also permit selectively connecting the perforated member to a vacuum source at the surface. Hydraulic control arrangements permit regulating the valves from the surface vessel to control the rate of removal of air or gas from the pipe.

Unite-1 States Patent [191 Santangelo et al.

[4 Oct. 16, 1973 THE SEA FLOOR Primary Examiner-Evon C. Blunk Assistant Examinerl-ladd Lane AttorneyJohn L. Sniado et a1.

[75] Inventors: Joseph G. Santangelo, Morristown,

N.J.; Marne A. Dubs, New Canaan, Conn.; Clifford E. Schatz, Solana [57] ABSTRACT Beach, Calif. A1r 1s wlthdrawn from an an 11ft hydraulic pipe to conl Assigneei Kenneco pp Corporation, trol turbulence and velocity of flow through the pipe. New York The air is withdrawn at a location substantially above [22] Filed: Jan. 21 1972 the air injection station where the expanding air causes excesslvely hlgh veloclty and turbulence whlch PP 219,623 cause nodule breakage and wear of the pipe. In one embodiment a sleeve valve is used to selectively open 52 us. (:1. 302/14, 417/108 Prforatims mmunicatihg with the interim [51] Int. Cl. B65g 53/30 Plpe' The body of the valve can be connected to a [58] Field of Search 302/66, 14, 15, 16; h some at the Surface Crease the ahmht 417/54, 108 of an removed from the plpe. In a second embodiment a perforated member is located within the pipe and [56] References Cited flolw of to tlhe ozltside of title tiipe is lcontrolledby UNITED STATES PATENTS va ves. e va ves so perml se ect1ve y connecting the perforated member to a vacuum source at the sur- 2; g h z-" 417/54 face. Hydraulic control arrangements permit regulatoun e a ing the valves from the surface vessel to control the 2,076,823 4/1937 Newell 302/14 X rate of removal of air or g from the p p FOREIGN PATENTS OR APPLICATIONS 95,839 1/1898 Germany 417/108 16 Clam, 4 Draw F'gures r 1 2 j E 513m Patented Oct. 16, 1973 2 Sheets-Sheet 2 PROCESS AND APPARATUS FOR TRANSPORTING MINED DEPOSITS FROM THE SEA FLOOR This invention relates generally to lifting materials from the floor of a body of water such as the sea floor,

and particularly to the transporting of mined mineraldeposits from the sea floor to a surface station. More specifically, the invention relates to the transporting of mined sur'ficial sediments such as manganese or phosphorite nodules from the sea floor to a surface vessel by means of an improved air lift hydraulic dredge technique.

A well known technique for transporting mined materials from the sea floor to the surface is the air (or gas) lift hydraulic dredge. In this air lift system, air or gas is injected into the dredge pipe or lift pipe at a location somewhat below the water surface and the injected air creates a lift effect which causes water and the mined particulate material to flow upwardly through the pipe. The depth at which the air or gas is injected depends on the depth at which the mining is done so the necessary velocities are created within the pipe to transport the particulate material to the surface.

The air lift system presents several problems. First, in deep mining, i.e., at depths of 10,000 feet, 15,000 feet or greater, it is necessary to inject the lifting air at some distance below the surface of the water, for example, 3,000 feet. A bubble of air at such depth will expand to almost 100 times its original volume during travel upwardly from the 3,000 foot depth to the water surface. In addition, 50 percent of the total expansion of the bubble will take place in the final 34 feet of the ascent, where the static head and back pressure on the bubble is the lowest. Such tremendous expansion in the final section of the pipe leads to unfavorable conditions such as a very high exit velocity of the transported material and extreme turbulence within the pipe.

The high exit velocity from the pipe has required the use of baffles and other equipment to decrease the exit speed of the mined material. Such baffles, however, tend to cause the mined material such as manganese nodules to break and otherwise disintegrate, making them more difficult to handle and to separate undesirable materials, such as sand from the nodules. In addition, the turbulence and high velocities within the pipe cause further disintegration of the nodules.

Applicants, in accordance with this invention, have devised a means to control the velocity and deleterious effects of the expanding air in the upper section of the lift pipe. This is accomplished by controllably removing air from the pipe at one or more locations along the length of the pipe above the location where the lift air is initially injected or introduced. By bleeding air or gas out of the pipe at a controlled rate at one or more selected locations, the expansion of the air or gas within the pipe is controlled and correspondingly, the exit velocity of the mined material as well as the velocity of the material within the pipe is controlled.

Correspondingly, the desired lift is obtained to cause a flow of water through the pipe at a sufficient velocity to transport the mined materials from a location below the point of injection of the lifting gas, a three-phase slurry of gas, water, and mined material exists in the pipe at a location above the injected gas, and the dea location below the uppermost portion of the pipe to control the expansion of the gas.

Correspondingly, an object of this invention is an improved gas or air lift hydraulic system for transporting particulate materials from locations on the sea floor.

Another object is an improved air lift hydraulic system for controlling the velocity of a slurry within an air lift pipe to reduce disintegration of particulate material transported by the pipe.

Another object is a unique control system for an air lift arrangement where the expansion of the lifting air or gas is controlled by bleeding air from the lift pipe at one or more selected locations along the length of the pipe but below the uppermost portion of the pipe.

A further object is an airlift system for transporting deposits in which a control valve at a pre-selected location along the lift pipe is used to bleed air or gas from the interior of the pipe.

A further object is a unique slidable valve arrangement in which the valve encircles the pipe and a low pressure region is maintained in communication with ports in the side of the pipe to withdraw air or gas from the pipe.

A further object is a method and apparatus in which flow means within the lift pipe below the location of controlled removal of air from the pipe cause the conveyed particulate material to be directed inwardly away sired velocities within the pipe are maintained by selectively removing some of the gas or air from the pipe at from the sides of the pipe whereby, the air or gas can be removed without interference by the particulate material.

A further object is a method and apparatus in which a porous element within the interior of the airlift pipe and spaced from the walls of the pipe is used to bleed excess air or gas from the pipe to control the flow velocities and turbulence within the pipe.

A further object is a method and apparatus in which the location of, the rate of, and the area of extraction of the air from the lift pipe are carefully controlled.

An additional object of the invention is a method and apparatus for controlling the flow rate and velocity within an airlift pipe by introducing air into the pipe at a predetermined constant rate and by bleeding air from the pipe at a location above the point of introduction to control the rate of flow of mined material through the pipe.

Numerous other features, objects, and advantages of the method and apparatus of this invention will become apparent with reference to the accompanying drawings which form a part of the specification and in which FIG. 1 is a schematic view in front elevation showing an underwater mining system in accordance with this invention;

FIG. 2 is an enlarged view in vertical section of the gas removal station of the system of FIG. 1;

FIG. 3 is a view corresponding to FIG. 2 showing a porous material sidewall section of the pipe; and

FIG. 4 is a view in vertical section and partly in schematic showing a second embodiment of gas removal station for the system of this invention.

Referring now to the drawings in detail and particularly to FIGS. 1 and 2 there is shown a first embodiment of the method and apparatus for mining and lifting surficial sediments and particulate materials such as manganese nodules from the bottom of a body of water. As shown at FIG. 1, a lift pipe or dredge conduit 1 is disposed in a body of water 2, the lower end of the lift pipe extending to the bottom 3 of the body of water. The

upper end 4 of the pipe is supported by a surface vessel 6 such as a ship or barge and extends to a location above the surface 7 of the water. Upper end 4 of the lift pipe extends over the vessel 6 and terminates at a downwardly opening outlet 8 via which sediments and other particulate material 9 removed from the ocean floor are discharged into the vessel. The upper end of the lift pipe may be supported from the vessel as by a support assembly 10 including a boom 12 and cables 13. At the bottom of the lift pipe is an inlet nozzle 14 which can be used as a dredge inlet or alternatively, the lower end of the lift pipe can be connected directly to a mining vehicle (not shown).

Mounted on vessel 6 is a source of air under pressure which advantageously takes the form of a motor driven compressor unit 15. Compressor unit 15 is connected to an air inlet section 16 of lift pipe 1 via a suitable hose or piping 17. The air inlet section of lift pipe 1 advantageously includes a sleeve 18 extending around and enclosing a section of the pipe having a perforated section 19 to inject compressed air or gas uniformly into lift pipe 1. The air introduced at the location of the inlet section 16 causes an upward flow of water through nozzle l4 and ultimately out of outlet 8. As the water enters the inlet at nozzle 14 the particulate material on the ocean floor is swept into the lift pipe. Sufficient air is introduced at inlet 16 to cause a flow through the pipe at a velocity sufficient to lift the nodules and convey them upwardly through the pipe.

A significant disadvantage of present air lift systems where the outlet 8 of the airlift pipe is open to atmosphere is that the injected air expands tremendously during its travel upwardly through the pipe because of substantial reduction in pressure between the location of injection and the discharge end of the pipe. As already mentioned, a bubble of air injected at 3,400 feet below the surface 7 will expand to approximately 100 times its original volume where the outlet of thepipe is at atmospheric pressure. In addition, 50 percent of the total expansion will take place in final 34 feet of the ascent, where the static head or back pressure is the lowest. Such tremendous expansion of air or gas in the lift pipe has in the past led to unfavorable conditions where the outlet of the pipe is open to atmospheric pressure. As a result, there is turbulance and a very high velocity of the slurry of air, water, and particulate material near the upper end of the pipe with existing air lift sytems.

The turbulence and high velocities in the pipe cause breaking and disintegration of the nodules which makes the nodules. more difficult to separate from other particulate matter drawn into nozzle 14. In accordance with the method and apparatus of this invention, these problems are substantilly reduced by removing some of the air or gas at a gas removal station 20 which is located above theinjection station 16 but is below the top of the upper end 4 of pipe 1. While only one gas removal station 20 is shown at FIG. 1, several such stations can be provided along the length of the pipe, and because of the expansion which occurs near the surface of the water, a station such as station 20 can be located above the surface of the water at a location 21.

FIG. 2 shows one embodiment of lift pipe 1 at gas removal station 20. At the gas removal station 20 a special section 22 of lift pipe is used which has a smooth polished outer surface and a perforated section having vertically spaced rows 23-27 of apertures 28 which extend through the side wall of pipe section 22.

Surrounding section 22 of the pipe is an elongated cylindrical sleeve 29. Formed in sleeve 29 is an annular recess which defines an annular chamber 30. The ends of chamber 30 are closed by inwardly projecting annular flanges 31 and 32 each of which has a suitable seal at its interior surface to seal against the outside surface 33 of the pipe. Above the chamber 30 is an annular second or cylinder chamber 34 separated from chamber 30 by flange 32. Chamber 34 has its upper end closed by a ring 35 secured to the top of sleeve 29, ring 35 having a seal at its inner surface which seals against the outside surface 33 of the pipe.

On section 22 of pipe 1 is an outwardly projecting piston ring 36 with a beveled peripheral surface and a circumferential seal 37 which seals against the inside wall 38 of chamber 34. Ring 36 functions as a fixed piston and sleeve 29 functions as a movable cylinder which slides axially along section 22 of lift pipe 1. Axial movement of sleeve 29 is controlled by introducing hydraulic fluid through either port 39 which is located immediately above flange 32, or port 40 which is located immediately below ring 35. Communicating with port 39'is a hydraulic flow line 41 connected to a pressure source 42 via a control valve 43. Similarly, connected to port 40 is a flow line 44 which communiates with pressure source 42 via a control valve 45. The pressure source 42 is located on vessel 6 as are control valves 43 and 45, so the position of the sleeve can be changed from the vessel.

Communicating with a chamber 30 is a flow line 46 which is connected to a vacuum tank 47 also located on vessel 6. A flow control valve 48 is located in line 46 adjacent vacuum source 47.

Sleeve 29 functions as a valve to selectively expose rows 23-27 of the ports 28 to the water surrounding section 22 of the pipe. Sleeve 29 is moveable between the upper or solid line position shown at FIG. 2 and the lower or dotted line position in which lower flange 31 extends below bottom row 29 of the perforations and upper flange 32 is above the top row 23 of the perforations. With the sleeve 29 in the dotted line position the perforations of rows 23-27 all communicate with chamber 30 and are isolated from the sea water surrounding section 22 of the pipe. On the other hand, with the sleeve in its upper position as shown at FIG. 2, the perforations of the rows 23-27 are all exposed and in communication with the water surrounding the pipe. It will be appreciated that sleeve 29 can be moved to any intermediate position between the solid line and dotted line positions so that only selected rows for example rows 23 and 24 communicate with chamber 30,

I the remaining rows 25-27 being exposed to the sea water surrounding the pipe.

Movement of sleeve 29 between the solid and dotted line positions is accomplished by introducing hydraulic fluid either above or below the ring piston 36. Opening valve 43 causes hydraulic fluid under pressure to flow from source 42 through line '41 and port 39 thereby causing the sleeve to move downwardly. To return the sleeve to the uppermost position shown in solid lines, valve 43 is vented and valve 45 is opened to introduce hydraulic fluid through port 40 into the portion of chamber 34 above piston 36 so'the sleeve moves upwardly.

With sleeve 29 in its lower dotted line position, and with valve 48 closed, the pressure in chamber 30 will equal the pressure within pipe 1 and there will be no flow through perforations 28 into chamber 30. When sleeve 29 is raised to the solid line position (or to some intermediate position where for example, rows 26 and 27 of perforations are exposed), some of the air flowing through the pipe will bleed out through these rows of perforations and correspondingly, the amount of air within the pipe will be reduced. The extent of bleed-off of the air can be controlled by moving sleeve 29 so only a selected number of rows of perforations are exposed. Where it is desired to bleed-off more air than can escape through the perforations of rows 23-27 with all these rows exposed, the sleeve 29 is moved downwardly so only several rows are exposed whereupon valve 48 is opened to connect vacuum source 47 to chamber 30. Such reduced pressure in chamber 30 will considerably increase the flow of air through perforations 28. Hence, by adjusting the position of sleeve 29 the amount of air which escapes through the perforations 28 can be regulated, and an increased amount of air can be removed from the pipe by connecting vacuum source 43 to chamber 30 when the sleeve is at an intermediate or lowest dotted line position.

In the region of pipe section 22, the material flowing through the pipe takes the form of a slurry of air, water, and particulate material. To prevent clogging of the perforations 28 as a result of allowing air to bleed through these perforations, a constrictor 50 is provided at the lower end of section 22 of the pipe to direct the particles slightly inwardly away from the inside surface 51 of the pipe, at the location of the rows 23-27 of perforation. The effect of the inwardly projecting constrictor 50 is to direct the particulate material inwardly slightly as shown by the arrows 52.

FIG. 3 shows a second embodiment of a portion of the section 22 of pipe 1. This section designated 22 is identical to section 22 in all respects save that the region of the rows 23-27 of perforations is replaced by a porous hollow cylindrical section 55 at the same location along the pipe as the rows of perforations. This porous section 55 can take the form of sintered metal or other foraminus material which is sufficiently porous to permit air to bleed from the inside of the pipe. Of course, the length of and porosity of section 55 of the pipe will be so selected that the same amount of air can be withdrawn as is withdrawn through the perforations 28 of rows 23-27. The porous section 55 can be used to advantage where relatively large sized particles are conducted through the pipe which could cause clogging of perforations 28 of the rows 23-27. On the other hand, where some very fine materials are in the slurry flowing through the pipe such fine materials could clog the porous materials of section 55, and under these conditions rows of the perforations 28 of a size to pass fines can be used to better advantage.

FIG. 4 shows a second embodiment of an apparatus for removing air from lift pipe 1. In the embodiment of FIG. 4 there is an air removing member 60 located within pipe 1 at a selected location above air inlet station 16. Member 60 takes the form of a hollow cylinder with a rounded lower end 61. Both the sides and lower end 61 of the tube are formed from either a porous material such as the porous material described for section 55 or alternatively, the sides and bottom can be provided with a plurality of perforations 62, as shown at FIG. 4, to permit air in pipe 1 to flow to the interior 63 of member 60. The upper end of member 60 is connected to transverse conduit 64 which extends through an opening in the wall of pipe 1 and both supports the member 60 and provides communication between the interior 63 and the exterior of pipe 1. Connected to conduit 64 at a location closely adjacent pipe 1 is a first flow control valve 65. Valve 65 includes a slidable valve element 66 which is operated by the piston 67 of hydraulic cylinder 68. Connected to the upper end of cylinder 68 is a flow line 69 which communicates with a source of pressure fluid 70 via a control valve 71. The lower end of cylinder 68 is connected to a line 72 which is connected to the hydraulic pressure source 70 via a control valve 73.

There is also a second flow control valve 74 beyond valve 65 and which is connected to an upwardly extending tee 75 which has an inlet connected to the outlet of valve 65. The outlet of valve 74 is in communication with the water surrounding pipe 1, and extends upwardly. The valve element 77 of valve 74 is remotely operated by hydraulic cylinder 78 via hydraulic lines 79 and 80 connected respectively to pressure source 70 via control valves 81 and 82. The outer horizontal leg of tee 75 is connected to a vacuum line 83 which in turn is connected to a vacuum source 84. As shown at FIG. 4, the control valves 71, 73, 81, and 82 as well as pressure source 70 and vacuum source 84 are located on the vessel 6.

The air bleed-off arrangement of FIG. 4 functions be removing air from pipe 1 at a location spaced from the inside surface 51 of the pipe. To prevent clogging of perforations 62 (or pores, where the member is made of a porous material) and to prevent the solids materials conveyed by the pipe from impacting against the bottom 61 of member 60 a conical deflector 86 is located within the pipe at a location just below member 60. Deflector 86 is supported by struts 87 which are advantageously streamlined, are secured to the inside of the pipe, and support the deflector 86 at a location along the axis of the pipe. The action of deflector 86 is to cause the particulate and other solids materials to be deflected outwardly as shown by the arrows 88. Hence, the solid and particulate material in the slurry flowing through pipe 1 is deflected outwardly around the member 60 and correspondingly, there is less clogging and abrasion of the member 60 from the material conveyed by the pipe. However, air can be withdrawn through the perforations 62.

The amount of air that bleeds out of the pipe through member 60 can be carefully controlled by manipulating flow control valves 65 and 74. If it is desired to communicate the member 60 with the water surrounding pipe 1, valves 65 and 74 are both opened, which can be accomplished remotely from vessel 6 by opening the valves 73 and 81. Opening these valves provides a path to outlet 76 which communicates with the water surrounding lift pipe 1 and permits air to bleed from the interior of the pipe into thesurrounding water. It will be appreciated that either or both the valve elements 66 and 77 can be placed in an intermediate position to control the extent of air bleed-off.

While it is desired to remove more air than will bleed through the outlet 76 when both valves 65 and 74 are opened, vacuum source 84 is actuated to produce a reduced pressure in vacuum line 83. Then, valve 65 is opened and valve 74 is closed so the vacuum source communicates directly with the interior 63 of the member 60. By virtue of the reduced pressure in the vacuum line 83 a larger quantity of air will be removed from the pipe 1.

In addition, it is contemplated that in the event that the perforations 28 of the embodiment of FIG. 2 become clogged, those perforations can be backflushed through flow line 46. Where it is necessary to periodically clean the perforations, a suitable valve and additional piping (not shown) will be provided at the surface nozzle 6 to backflush the perforations with either water or compressed air. Similarly, the perforations 62 in the member 60 can be backwashed or backflushed by applying flushing air or water through flow line 83 from a suitable pressure source at surface vessel 6. The frequency of such backflushing will, of course, depend on the nature of the slurry in the lift pipe as well as on the amount of air that is removed at the air removal stations.

It is further contemplated that under certain conditions, some water will flow through the perforations as air is removed from the lift pipe at an air removal station. Such bleed off water, should it accumulate in chamber 30 of the embodiment of FIG. 2, or in the flow line 83 of the embodiment of FIG. 4 can, of course, be periodically dumped by providing suitable vent valving or can be pumped from the regions of collection as is necessary. Alternatively, backflushing with air under pressure through the respective flow lines 46 or 83 of the respective embodiments of FIGS. 2 and 4 will expell all accumulated water from each of the systems.

By bleeding air or gas from the interior of the pipe in the manner explained for either the embodiments of FIG. 2 or FIG. 4, the velocity of the slurry flowing through the pipe can be carefully controlled and can be maintained at a sufficiently high level to convey nodules of substantial size while maintaining turbulence at a minimum. In addition, the exit velocity of the slurry at the outlet 8 can be substantially reduced with a corresponding reduction in wear of the piping as well as a reduction in breaking and disintegration of the nodules both within the pipe and as they discharge on the pile of material 9. Such control can be accomplished by injection of air into the inlet station 16 at a constant rate and bleeding air out of the pipe at station 20 to control the velocity of flow through the pipe. correspondingly, velocity in the lower portion of the pipe can be maintained at a high enough value to lift even large nodules.

While several preferred embodiments of the apparatus of this invention have been described in detail, and while several techniques for bleeding air from an air lift hydraulic system to control the flow velocities within the pipe have also been described, it is to be understood that changes can be made from the techniques disclosed herein without departing from the scope of this invention as set forth herein and in the appended claims.

What is claimed is:

1. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea;

gas introducing means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material;

gas removal means to remove gas from the pipe at a location substantially above its location of introduction by said gas introducing means; and control means to control the gas removal means to remove only a portion of the gas introduced by the gas introducing means so that the velocity of material flowing through the pipe can be regulated. 2. An airlift system according to claim 1 wherein said means to introduce a gas into the pipe is located below the surface of the sea; and said means to remove gas from the pipe is located below a collection station at the surface of the sea. 3. An airlift system according to claim 1 wherein said means to remove gas from the pipe includes passage means communicating with the interior of the pipe,

valve means associated with said passage means to control the flow of gas through the passage means; and

said control means includes means to control the valve means to regulate the removal of gas from the pipe.

4. An airlift system according to claim 3 wherein said passage means include a porous member in communication between the interior and exterior of the pipe, and

said valve means includes a valve for controlling the flow of gas from said porous member to the exterior of the pipe.

5. An airlift system according to claim 4 wherein said porous member is located in the side wall of said pipe.

6. An airlift system according to claim 3 wherein said means to remove gas further includes means to create a low pressure region communicating with said passage means.

7. A process for continuously transporting particulate material upwardly through a pipe in a body of water while controlling the velocity of the material through the pipe comprising introducing gas into a pipe having an inlet below the water surface to induce a flow of water through the pipe at a velocity sufficient to transport the particulate material;

controlling the removal of at least a portion of the gas from said pipe at a location above the location of introduction of the gas and below the uppermost portion of the pipe to control and regulate the velocity of the material flowing through the pipe.

8. A process according to claim 7 wherein said step of removing gas from the pipe includes creating a lowpressure region communicating with the interior of the pipe and I removing gasfrom said low presure region.

9. A process for transporting material according to claim 7 wherein said step of removing gas from the pipe includes creating a low pressure region adjacent the outside surface of the pipe, and

removing gas through apertures in the wall of the pipe communicating with said low pressure region. i

10. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea;

means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material;

means to remove gas from the pipe at a location above its location of introduction by said gas introducing means;

said means to remove gas from the pipe includes passage means communicating with the interior of the pipe, and

valve means associated with said passage means to control the flow of gas through the passage means;

said passage means include a plurality of openings formed in a wall of said pipe; and

said valve includes a casing concentric with and moveable along said pipe to selectively cover and uncover said openings. 11. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particlate material;

means to remove gas from the pipe at a location above its location of introduction by said gas introducing means;

said means to remove gas from the pipe includes passage means communicating with the interior of the pipe, and valve means associated with said passage means to control the flow of gas through the passage means; said passage means include a porous member in communication between the interior and exterior of the pipe;

said valve means includes a valve for controlling the flow of gas from said porous member to the exterior of the pipe; and said porous member is within said pipe. 12. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material;

means to remove gas from the pipe at a location above its location of introduction by said gas introducing means; said pipe has a side wall including passage means extending between the interior and the exterior of the P p said means to remove gas from the pipe includes a sleeve extending around said pipe in the region of said passage means, said sleeve being slidable along said pipe, means to remove said sleeve to a pre-determined location relative to said passage means to selectively cover and uncover said passage means, and means communicating with said sleeve to create a low pressure region within said sleeve; whereby said passage means can be selectively placed in communication with the interior of said sleeve by operating said sleeve moving means. 13. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material;

means to remove gas from the pipe at a location above its location of introduction by said gas introducing means;

said means to remove gas from the pipe includes passage means within said pipe and in communication with a conduit outside the pipe,

a region of low pressure connected to said conduit,

and

valve means for regulating gas flow from said passage means to said low pressure region via said conduit.

14. An airlift system according to claim 13 wherein said means to remove gas from the pipe further includes second valve means in said conduit for communicating said conduit with a region at the exterior of said pipe.

15. A process for transporting particulate material upwardly in a body of water comprising introducing gas into a pipe having an inlet below the water surface to induce a flow of water through the pipe at a velocity sufficient to transport the particulate material;

removing at least a portion of the gas from said pipe at a location above the location of introduction of the gas and below the uppermost portion of the p p said step of removing gas from the pipe includes creating a low pressure region communicating with the interior of the pipe, and

controlling the flow of gas from the pipe to said low pressure region.

16. A process according to claim 15 wherein said step of controlling the flow of gas to said low pressure region includes controlling said flow of gas from a control station at the surface of the water. 

1. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; gas introducing means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material; gas removal means to remove gas from the pipe at a location substantially above its location of introduction by said gas introducing means; and control means to control the gas removal means to remove only a portion of the gas introduced by the gas introducing means so that the velocity of material flowing through the pipe can be regulated.
 2. An airlift system according to claim 1 wherein said means to introduce a gas into the pipe is located below the surface of the sea; and said means to remove gas from the pipe is located below a collection station at the surface of the sea.
 3. An airlift system according to claim 1 wherein said means to remove gas from the pipe includes passage means communicating with the interior of the pipe, valve means associated with said passage means to control the flow of gas through the passage means; and said control means includes means to control the valve means to regulate the removal of gas from the pipe.
 4. An airlift system according to claim 3 wherein said passage means include a porous member in communication between the interior and exterior of the pipe, and said valve means includes a valve for controlling the flow of gas from said porous member to the exterior of the pipe.
 5. An airlift system according to claim 4 wherein said porous member is located in the side wall of said pipe.
 6. An airlift system according to claim 3 wherein said means to remove gas further includes means to create a low pressure region communicating with said passage means.
 7. A process for continuously transporting particulate material upwardly through a pipe in a body of water while controlling the velocity of the material through the pipe comprising introducing gas into a pipe having an inlet below the water surface to induce a flow of water through the pipe at a velocity sufficient to transport the particulate material; controlling the removal of at least a portion of the gas from said pipe at a location above the locAtion of introduction of the gas and below the uppermost portion of the pipe to control and regulate the velocity of the material flowing through the pipe.
 8. A process according to claim 7 wherein said step of removing gas from the pipe includes creating a low pressure region communicating with the interior of the pipe and removing gas from said low pressure region.
 9. A process for transporting material according to claim 7 wherein said step of removing gas from the pipe includes creating a low pressure region adjacent the outside surface of the pipe, and removing gas through apertures in the wall of the pipe communicating with said low pressure region.
 10. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material; means to remove gas from the pipe at a location above its location of introduction by said gas introducing means; said means to remove gas from the pipe includes passage means communicating with the interior of the pipe, and valve means associated with said passage means to control the flow of gas through the passage means; said passage means include a plurality of openings formed in a wall of said pipe; and said valve includes a casing concentric with and moveable along said pipe to selectively cover and uncover said openings.
 11. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material; means to remove gas from the pipe at a location above its location of introduction by said gas introducing means; said means to remove gas from the pipe includes passage means communicating with the interior of the pipe, and valve means associated with said passage means to control the flow of gas through the passage means; said passage means include a porous member in communication between the interior and exterior of the pipe; said valve means includes a valve for controlling the flow of gas from said porous member to the exterior of the pipe; and said porous member is within said pipe.
 12. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material; means to remove gas from the pipe at a location above its location of introduction by said gas introducing means; said pipe has a side wall including passage means extending between the interior and the exterior of the pipe; said means to remove gas from the pipe includes a sleeve extending around said pipe in the region of said passage means, said sleeve being slidable along said pipe, means to remove said sleeve to a pre-determined location relative to said passage means to selectively cover and uncover said passage means, and means communicating with said sleeve to create a low pressure region within said sleeve; whereby said passage means can be selectively placed in communication with the interior of said sleeve by operating said sleeve moving means.
 13. An airlift-hydraulic system for transporting particulate material from the sea floor comprising, in combination a pipe having an inlet below the surface of the sea; means to introduce a gas into the pipe to cause an upward flow of water through the pipe at a velocity sufficient to transport the particulate material; means to remove gas from the pipe at a location above its location of introduction by said gas introducing means; said means to remove gas from the pipe includes passage means within said pipe and in communication with a conduit outside the pipe, a region of low pressure connected to said conduit, and valve means for regulating gas flow from said passage means to said low pressure region via said conduit.
 14. An airlift system according to claim 13 wherein said means to remove gas from the pipe further includes second valve means in said conduit for communicating said conduit with a region at the exterior of said pipe.
 15. A process for transporting particulate material upwardly in a body of water comprising introducing gas into a pipe having an inlet below the water surface to induce a flow of water through the pipe at a velocity sufficient to transport the particulate material; removing at least a portion of the gas from said pipe at a location above the location of introduction of the gas and below the uppermost portion of the pipe; said step of removing gas from the pipe includes creating a low pressure region communicating with the interior of the pipe, and controlling the flow of gas from the pipe to said low pressure region.
 16. A process according to claim 15 wherein said step of controlling the flow of gas to said low pressure region includes controlling said flow of gas from a control station at the surface of the water. 